(see Figure REF ). The sizes of \({\mathbf {H}}_1\)  in the [1]} case, and of \({\mathbf {H}}_1\)  and \({\mathbf {H}}_2\)  in [2]} are chosen to ensure unicity of the representation of an element of a list as the sum of two elements of the lists used for the merge (this is the representation technique).
<FIGURE>